1. Field of the Invention
The invention relates to a straight motorized handpiece, in particular for medical purposes, preferably for a medical or dental laboratory, with a clamping device which is arranged in a sleeve-like casing for the selective clamping of tools which can be inserted from the front into the handpiece. The clamping device is arranged on a drive shaft which is rotatably mounted in the casing by means of rearwardly and forwardly located roller bearings whereby, for axially retaining the drive shaft, a first shoulder is provided on the casing or on attachments thereto, against which there bears the outer ring of one of the roller bearings, and a releasable arresting shoulder is located opposite to the first shoulder at an axial spacing therewith.
A handpiece of the kind concerned is in particular suitable for that kind of mechanical work on natural or artificial parts of the human or animal body for which a comparatively large drive and working power is required. In the medical field such a handpiece is thus particularly suitable for work on comparatively solid parts of the body. In the dental field such a handpiece may be used for dental treatment in the oral cavity of a patient, if it is of correspondingly small construction.
A handpiece of the kind concerned is preferably suited for a medical, in particular dental laboratory, in which in particular artificial body parts or models are machined by means of rotary tools which can be clamped into the handpiece. The handpiece is suitable for the transmission of a comparatively large working power to the tool, and different tools may rapidly and readily be mounted or released and exchanged.
2. Discussion of the Prior Art
A handpiece of the kind mentioned in the introduction is marketed by the assignee under the designation K9-Handpiece Type 950 and is thus known. In the following this handpiece will be described with reference to FIG. 5.
The rod-shaped straight handpiece 1 comprises a rearward motor part 2, which is only partly illustrated, with an in particular electrical drive motor 3 mounted therein, and a forward handpiece part 4 into which, from the front, a working tool can be mounted with its shaft 5. For this purpose there serves a sleeve-like, slotted clamping chuck 6, which is part of a drive shaft 7, which is rotatably mounted coaxially in the handpiece part 4 and is connected with the drive motor 3 for rotation. The clamping chuck 6 can be opened and closed by means of a relative rotation between the motor part 2 and a grip sleeve 4a of the handpiece part 4. For this purpose an actuating mechanism 8 is integrated into the handpiece part 4, which mechanism is effective between the grip sleeve 4a and the drive shaft 7 and has a transmission 9 which converts the rotary movement of the grip sleeve 4a into an axial movement of a round draw rod 10, which extends from the rear coaxially through a bearing sleeve 7a of the drive shaft 7, is mounted therein axially displaceably in a bore and is screwed into an internal thread 6a of the clamping chuck 6 with its forward end. The grip sleeve 4a is mounted on a sleeve-like internal casing 11 to be rotatable around the longitudinal middle axis 12 of the handpiece 1 and to be longitudinally displaceable. In the internal casing 11, the drive shaft 7 is rotatably mounted by means of two roller bearings 13, 14 which have an axial spacing from one another, of which the forward roller bearing 14 bears against an internal annular shoulder 15 of the internal casing 11 with its rear side, whereby the outer ring of the roller bearing 14 is fixedly screwed against the internal ring shoulder 15 by a nut 16. The nut 16 is screwed into an internal thread at the forward end of the internal casing 11. Further, a front cap 47 is screwed into the internal thread in front of the nut 16, which cap covers the clamping chuck 6 approximately half of which projects from the internal casing 11.
The transmission 109 has a radial screw 17, which penetrates a radial hole in the grip sleeve 4a and, with a roller 18 penetrates a groove 19 in the internal casing 11 which runs obliquely in the circumferential direction, and is screwed into a pressure piece 21, which sits axially displaceably--with play for movement--in the rear end region of the hollow cylindrical internal casing 11 and has a central hole 23 in a middle inner ring 22, through which hole the drive shaft 7 projects with a plug-in connection section 24, which is connected with a drive pin 26 of the drive motor 3 by way of a plug-in coupling 125.
The motor part 2 also has an internal casing 27, in which the drive motor 3 is arranged and with which casing the motor part is screwed on to the rear end of the internal casing 11 of the handpiece part 4, at 28, whereby the grip sleeve 4a rearwardly overlaps the forward end of the motor part 2.
With this known handpiece the drive shaft 7 is, in the regions which lie behind the internal ring shoulder 15, greater in cross-section than the free internal cross-section of the internal ring shoulder 15.
After certain periods of use of the handpiece it is necessary to exchange the bearings 13, 14 of the drive shaft 7, as they are subjected to unavoidable wear-and-tear. For this purpose the drive shaft 7 must be de-mounted, which is effected by the following de-mounting measures:
The handpiece part 4 is to be separated from the motor part 2, which is effected by unscrewing the screw connection 28 between them.
The screw 17 is to be released by means of a spanner and to be removed with the roller 18.
Then, the internal casing 11 can be rearwardly withdrawn from the grip sleeve 4a.
In a further de-mounting step, the pressure piece 21 is to be rearwardly withdrawn from the internal casing 11, after previously or now unscrewing the front cap.
For de-mounting the roller bearing 14, a Quad-ring 29 and a disk 31 are further to be removed. Thereafter, the nut 16 is to be loosened with a spanner and unscrewed. In a next de-mounting step, the drive shaft 7 is to be urged rearwardly, completely out of the interior casing 11, for which purpose a suitably adapted tool is helpful. Hereby, a bush 32 which is arranged before the roller bearing 14 is also urged out by the drive shaft 7.
Then, the draw rod 10 supporting the plug-in connection section 23 can be rearwardly screwed out of the drive shaft 7.
After removal of a securing ring 33 by means of a pair of Seeger circlip tongs the rear roller bearing 13 can then be drawn off the bearing sleeve 7a with a draw-off device.
The forward roller bearing 14 can also be drawn off the inner casing 11 with a draw-off device.
Through this known configuration, great manufacturing outlay and in particular a great outlay in terms of mounting effort and time is inevitably involved in the exchange of the bearings 13, 14.